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Democrats see the Pennsylvania seat as one of their prime pickup opportunities in the Senate in 2016

Washington (CNN)The Pennsylvania Senate primary got a little more crowded on the Democratic side Tuesday, but the national party continues to hold off on anointing a candidate.

Democrats see a challenge to incumbent Sen. Pat Toomey, R-Pennsylvania, as one of their prime pickup opportunities in the Senate in 2016 but have struggled to coalesce behind a challenger.

Longtime Democratic operative Katie McGinty officially declared her entry into the primary Tuesday, as expected, releasing a three-minute campaign video highlighting her work as chief of staff to Gov. Tom Wolf and Pennsylvania-native family biography.

But minutes after her official announcement went out to the media, the communications director for the Democratic Senatorial Campaign Committee tweeted that the party has not picked a horse.

"We're excited about the candidates we have in PA and look forward to running a strong campaign that turns Pennsylvania blue in 2016. #pasen," Justin Barasky wrote.

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McGinty joins former Rep. Joe Sestak, D-Pennsylvania, in the primary. Sestak declared his candidacy in March, but the party has held off from throwing its full support behind him.

Sestak drew Democrats' ire when he primaried former Pennsylvania Democratic Sen. Arlen Specter in 2010, defeating the party-switching incumbent only to lose to Toomey in the general election.

McGinty has a long history in national and state Democratic politics. She joined Wolf's administration after losing to him in the gubernatorial primary, and previously worked in the Clinton administration and Gov. Ed Rendell's administration on environmental issues. She's been expected to join the race for weeks, and resigned from the governor's office to clear her path late last month.

Sestak has struggled in the polls against Toomey. The most recent Quinnipiac poll in June had him trailing 47% to 36%. McGinty wasn't polled, though Wolf had positive approval ratings in the survey.

In her announcement video, McGinty ran through a list of national and state Democratic priorities, including affordable health care, job training, raising the minimum wage, equal pay for women, clean energy, unfair trade practices and college affordability.

"We need partners in Washington to help solve problems, not make them worse," McGinty said. "Unfortunately, Sen. Pat Toomey has become part of that Washington mess and has left middle class families out and behind."

The National Republican Senatorial Committee was also quick to jump on the announcement, slamming McGinty's record and entrance into the race.

"Pennsylvania Democrats are so dissatisfied with Congressman Joe Sestak's candidacy that they are now placing their bets on someone who finished dead last in a four-way Democratic gubernatorial primary last year," NRSC spokeswoman Andrea Bozek said in a statement. "It's bad enough that McGinty is one of the main proponents of the largest tax hike in Pennsylvania history, but her decision to pursue her own political ambitions instead of continuing to work to solve Pennsylvania's budget problems is proof positive she values her own self interest above that of Pennsylvania's interests."